ELECTROCYCLIC RUCTIONS OF AZIRIDINES by MUHAMMAD HUMAYOUN AKHTAR M. Sc., University of Moncton, 1966. A DISSERTATION SUBMITTED IN PARTIAL FULFILLMENT OF THE REQUIREMENTS FOR THE DEGREE OF DOCTOR OF PHILOSOPHY in the Department of Chemistry @ WHAMMAD HUMAYOUN AKHTAR , 1970 SIMON FRASER UNIVERSITY August, 1970 A PPR OVA L Name : Muhammad Humayoun Akhtar Degree : Doc tor of Philosophy Title of' Thesis: Electrocyclic Reactions of Aziridines Examining Committee: ,, A. C . Oehlschlaire'u' Senior supervisa/ . .- ' A. G. SherviooP Examining Committee - - K. ?I.Slessor ~xami~kn~Committee A. Fischer External Examiner Professor Department of Chemistry The University of Victoria Victoria, British Columbia Abstract Temperature dependent nmr spectra have been observed for a series of para-substi tuted 1-aryl-3,3- dimethyltriazenes . The temperature dependence has been interpreted in terms of restricted internal rotation about the N2,Fj bond of these triazenes and activation para- 5 meters AF', AH', and AS have been calculated from the spectral data. The origin of the rotational barrier is considered to lie in partial double bond formation between hT2 and T3 due to the contribution of 1,3-dipolar resonance hybrids to the qround states of these triazenes. This interpretation is supported by a sizable substituent effect o= -2'1 for the rotational process in the series studied. Chemical shift data at low temperatures indicates a stereo- specific association of benzene with the triazenes studied which places the benzene ring closer to the trans N-Me group in the 1,3-dipolar resonance hybrid. The thermal decomposition of ~T-arylazoaziridines follows two routes; one giving arylazide and alkene (stereospecif ically) and the other giving products typical of homolysis of the azo-linkage. The products of the homolytic route in benzene solvent are aziridines, biaryls and arenes. 30th the rate and extent of azide and alkene formation are favoured by increasing the electronegativity of substituents in the aryl ring and performing the reaction in more polar solvent (CHCL3 ) . Pyrolysis and photolysis of M-arylazo derivatives of larger cyclic amines proceeds via homolysis of the azo linkage to the exclusion of fragmenta- tion of azide and unsaturate. iii The thermal reaction of N-aryl-2,3-diphenyl aziridines with activated alkenes such as dimethyl maleate and dimethyl fumarate has been shown to yield 2,5-diphenyl- 3,4-dicarboalkoxy pyrollidines . The reaction is stereospeciflc with respect to the alkene reactant. Kinetic investigatton of the reaction revealed a two step reaction. The first step is considered to be rate determining conrotatory ring opening via C-C bond cleavage. A Hamrnett reaction constant of p = -0.8 was determined for the PI-substituents in this step. The second step is the concerted l,3-dipolar cyclo- addition of the ring opened aziridine of the alkenes. The reaction of 7-aryl-6a, 7a-dihydro-acenaphthai.[l, 2-b] - aziridines with alkenes proceeds via slow disrotatory ring opening via C-C bond cleavage (p = +0.74) with subsequent stereospecif ic 1,3-addi tion to alkenes . TO MY PARENTS Acknowledgment The author wishes to express his profound gratitude to his Research Director, Professor Allan C. Oehlschlager, for his guidance and advice during the course of this work. Thanks are also due to: "The inhabitants of Lab 7032" for many helpful and lively discussions; Professor T. Sorenson and Mrs. C. Jenkins of University of Calgary for 100 MHz nmr spectra; Professor J. Farmer of University of British Columbia for the use of esr spectrometer; Professor W. Lwowski for a sample of 3,3-biscyclo- hexenyl ; Mrs. R. Oehlschlager, and Mrs. M. Blazevich for typing the manuscript of this dissertation; Dr. Dennis Harris, Ophthalmologist, and the employees of Columbian Hospital for extraordinary attention provided during treatment; The faculty and staff of the chemistry department of Simon Fraser University for providing comradeship and encouragement ; And, the National Research Council of Canada for providing generous support of this work. -Table of Contents Page Abstract iii Chapter I Nmr Study of Hindered Rotation in 1-Aryl-3,3-dimethyltriazenes Introduction Results Discussion Experimental Chapter I1 Decomposition of N-Arylazoaziridines and Related Cycloamines Introduction Results Discussion Experimental Chapter I11 Cycloaddition of Aziridines to 27 and 47 Systems Introduction Outline of Present Study Results Discussion Summary Experimental Appendix Bibliography List of Tables Page Table I Chemical Shifts and Coalesence Temperatures of Triazene N-Methyl Hydrogens 7 Table I1 Activation Parameters from Line Measurements 8 Table I11 Properties of Triazenes 17 Table IV Products of Decomposition of N-Aryl- azoaziridines in Benzene and Chloroform 25 Table V Rates of Aryl Azide Formation from N-Arylazoaziridines in Benzene and Chloroform 27 Table VI Product Distribution from Pyrolysis and Photolysis of N-Arylazocycloamines in Benzene Solution 29 Table VII Properties of N-Arylazoaziridines 47 Table VIII Identification of Products of Thermal Decomposition of 11-13a,b, d, and e in Benzene 50 Table IX Spectral Chararacte'ristics of N-2-Chloro- ethyl anilines 52 viii Page Table X Chemicalshifts (6-values) of Ring Protons of l-Phenyl-2,5Ll,8-~a~hthal- Pyrrolidines 89 Table XI Chemical Shifts (6-Values) for Substituents at 3, and 4 Position of 1-Phenyl-2,5[ 1,8-~aphthal-~yrrolidines 98 Table XI1 Chemical Shifts (6-Values) of Diene Adducts of Aziridines 111-25a,d, and f 108 Table XI11 Comparison of Chemical Shifts of Adducts 111-35 and 111-62 111 Table XIV Chemical Shifts (&-Values) and Coupling Constants (Hz) for 1,2,5-Triphenyl- Pyrrolidines Table XV Chemical Shifts (6-Values) and Coupling Constants of 1-Alkyl-2-Benzoyl-5-Phenyl Pyrrolidines Table XVI First-order Rate Constants for the Reaction of tP-3 Aziridines 111-25a-f with Dimethyl Acetylenedicarboxylate ( DMAD ) 130 Table XVII First-order Rate Constants for the Reaction of Aziridines 111-2ga-d and Dimethyl Acetylenedicarboxylate at 110 .lo ix Page Table XVIII Yields, Melting Points, and Analyses of N-~ryl-6b,7a-~ihydro-acena~htha [l, 2-b]-Aziridines 162 Table XIX Spectral Data of N-~ryl-Gb,Ta- Dihydro-Acenaphtha[1,2-b]-Aziridines 164 Table XX Physical Properties of Aziridines 111-2ga-d, 111-30a,b and 111-3la,b 165 Table XXI Physical Properties of Adducts of 111-33b-f 192 Table XXII Physical Properties of Adducts 111-113a-d 193 List of Figures Page Figure 1 Plots of log k/T vs 1/T for 1-Aryl- 3,3-dimethyltriazenes in Chloroform 9 Figure 2 Correlation of log kx/kH and ox for the N-methyl interchange in 1-Aryl- 3,3-dimethyltriazenes 10 Figure 3 Plot of Av for the N-methyl signals of Triazenes as function of mole Percent of C6H6 in CDCIS 15 Figure 4 Plot of Absorbance (infrared) vs the Concentration of p-Nitrophenyl Azide in Benzene 56 Figure 5 Plot of Rate of Formation of p-Nitro- phenyl Azide on Thermal Decomposition 0 of 11-13c in Benzene at 70 Figure 6 Nmr Spectrum of Aziridine-dimethyl maleate Adduct 111-39 Figure 7 Nmr Spectrum of Aziridine-dimethyl muconate ~dduct111-62 Figure 8 Nmr Spectrum of Aziridine-2,Q- hexadiene Adduct 111-73 Page Figure 9 Correlation of log kx/kH and ox for the Decomposition of N-Aryl-2,3- diphenylaziridines Figure 10 Correlation of log kx/kH and ox for the Decomposition of Bicyclic Aziridines (111-25a-f) xii CHAPTER I NMR STUDY OF HINDERED ROTATION IN 1-ARYL- 3,3-DIMETHYLTRIAZENES ---Introduction In order to lay a foundation on which to base the study of the fragmentation of N-arylazoaziridines described in chapter 11. We studied the variable temperature nmr spectra exhibited by 1-aryl-3,3-dimethyltri~zenes . In general, amine derivatives which possess fl- conjugative systems directly attached to nitrogen, 1-1, exist partially as the 1,3-dipolar resonance structures, 1-2, and may be represented as 1-3. An observable effect of such resonance hybridisation is an increase in the effective barrier to rotation about X-N bond. This occurs to an appreciable extent in derivatives in which the dipolar resonance structures 1-2 are stabilized by the presence of electronegative substituents at the Y 1 position. Amine derivatives such as amides (x=c, Y=o), 2 nitrosoami ?es (x=N, Y=O) , enamines3 (x=Y=C ) , hydrazones 3 5 (X=N, Y=C) , amidines4 (X=C, Y=N), thioamides (x=c, Y=S ), 6 and selenamide (x=c, Y=s~), exist to a sufficient extent in the 1,3-dipolar structure, 1-2, to cause the barrier (7-23 Kcal) to rotation about the X-N bond to be measurable by nmr techniques. We have found thet 1-aryl-3,3-dimethyltriazenes 1-4 produced upon the coupling of aryl diazonium salts with 7 dimethylamine are excellent models for the study of the 1-1-1-2 resonance hybridization. Results Each of the para substituted triazenes listed in Table I exhibited temperature variable nmr spectra which were interpretable in terms of hindered internal rotation about the N2,N3 bond of 1-4. The N-methyl signals in the nmr spectra of the triazenes studied (see Table I) appeared as a single peak at room temperature. At lower temperatures the signals broadened and eventually emerged as two distinct signals of equal intensity. This type of temperature dependence may be described, vide infra, as a case of hydrogen exchange between two sites with equal populations and life- times. The temperature dependence was examined by the line width method above and below the coalesence temperatures. The rates of the exchange process were estimated above the coalesence temperatures using equation 1.2,8 In this equation 5 AV is the seperation of the N-methyl signals when the rate process is slow and W is the exchange broadening, i.e., the width of the methyl signals at half height.